It was based on a group of chimps that moved from a Dutch safari park to Edinburgh Zoo.
Now, three researchers have written to the journal Current Biology suggesting the results don't stack up.
The original team has responded, and stands by its findings and conclusions.
"There are a number of problems with the original study," said Dr James Higham, from New York University. "Some of these relate to the methods used, while others are fundamentally a misrepresentation of what the data actually show.